Bearing alloys



y 1961 E. PELZEL 2,982,677

BEARING ALLOYS Filed Oct. 10, 1957 Temp. "C

Zh %Al [/7 ven 75r inc/7 Pe/ze/ 2 United States Patent BEARING ALLOYS Erich Pelzel, Stolberg, Rhineland, Germany, assignor to Vereinigte Osterreichische Eisenund Stahlwerke Aktiengesellschaft, Linz-Donau, Austria, an Austrian company Filed Oct. 10,1957, Ser. N0. 689,374

13 Claims. (Cl. 148-13) Many binary alloys in the solid state consist of mixed crystals,'i.e., atomic solutions which exist only within a definite temperature range.

Similiar relationships occur in the zinc/aluminium system with an aluminium content above 17% A1. In the accompanying drawing, a section of the zinc/aluminium phase diagram is illustrated. Alloys over 17% Al solidify to B mixed crystals, line ab. If the proportion of aluminium is between 17 and 21%, the zinc crystals precipitate on further cooling, whereas the aluminium content of the ,8 mixed crystals increases to 21% Al, line a-c. This step is completed at 275 C. At this temperature, the [3 mixed crystals decompose to a eutectoid C. Alloys with more than 21% Al decompose on further cooling, line c-d, to two kinds of mixed crystals, that having the higher Zn content likewise de composing to the eutectoid C at 275 C. Aluminium/ zinc alloys with an aluminium content between 17 and 21% hence consist of zinc crystals and eutectoid, of 21% of only eutectoid and above 21% of eutectoidand aluminium-rich a mixed crystals.

With pure aluminuim/zinc alloys, the eutectoid decomposition occurs rapidly, but is hindered by additions of Mg, Cu and similar elements.

Quenched alloys show increased strength properties, quenching after longer heating above 275 C. thus representing an improvement step.

Alloys which largely or wholly consist of ,8 mixed crystals have proved suitable as hearing alloys. In particular, with alloys with more than 30% A1, a Cu content of /6 to A of the Al content and the remainder zinc, a reduction in strength and hardness by destructive heating between 80 and 280 C. causes a surprising improvement in bearing properties, if it is assumed that these include a lower coefiicient of friction and increased emergency running properties. Also in oil-less running, shafts and journals are not worn away, whereas this is the case with improved alloys and those which were rapidly cooled by casting.

Furthermore, a bearing alloy with an Al/Cu/Zn basis was proposed, which contained 3-l5% Al, 0.001-2% Cu, 0.01-0.06% Mn and as the remainder zinc with less than 0.01 each of Sn, Pb and Cd. This alloy shows no marked emergency running properties.

It was also known that alloys with 80-85% Zn, l4-

19% Al and l-2% Cu or with 80-85% Zn, 14-18% Al and 0-6% Cu exhibit unusual tensile strength and hardness and are especially suitable for manufacturing die cast articles, drawn rods and sheets.

It has now been found that alloys with l6-29% Al and certain copper contents, remainder zinc, give good bearing materials if the destructive heating is carried out suitably. This was surprising to the technician, since it was previously believed with high aluminium contents that there was a proportion of a mixed crystals, which in the alloy range according to the invention. is slight or even nil. In this range, the eutectoid structure is mainly prevalent. All attempts to use alloys according to the invention as hearing materials fail on the lesser emergency running property, since the importance of the destructive heating is not recognised. It is shown namely that with copper-containing alloys .with more than. 16% Al the natural cooling in sand or permanent molds is insufficient to lead to decomposition into a fine-grained eutectoid, and the cooled alloy must be subjected to a subsequent heating from room temperature.

' An example shows the effect. An alloy of 21% Al,

5% Cu and 74% Zn (99.99% pure) was cast into billets a ment under a constant bearing pressure and velocity with in a sand mould. The strength test gave a breakage strength of 40 kg./mm. an elongation of 5% and a Brinell hardness of 130 kg./mm. Bushes were made from the billets and were run in a corresponding arrangeoil lubrication. After closing ofi the oil supply, the

temperature of the bearing rose from 60 C. to 320 C. in 80 seconds, the bearing journals were worn and the machine stopped. The same alloy was subjected to a 12- hour heating at 200 C. The mechanical properties had worsened. The breakage strength was 30 kg./mm. the elongation 5% and the Brinell hardness only 100 kg./ mm. Bushings were made from the billets and subjected to the same running test. On closing off the oil supply, the temperature rose from C. to 220 C., but

only after 300 seconds, the friction resistance strongly increased and a grey, greasy paste formed on the bearing surface, so that no wearing of the journal occurred.

The example shows that the heating causes a lessening of the mechanical properties, but also a definite improvement of the bearing properties.

The method of manufacturing bearing alloys with good emergency running properties by heating zinc/aluminium/copper alloys at temperatures between 150 and 275 C. gives the bestresults with alloys of l629% Al, a copper content which is between and A of the aluminium content and is at least 2.2% and the remainder zinc (99.99% pure). 20 and 22% A1, a copper content of to A of the aluminium content and the remainder zinc give a considerable emergency running capacity, wherein the alloy mentioned in the example with 21% Al, 5% Cu, 74% pure zinc shows in sand moulding and chill moulding and also in the pressed state the optimum emergency running ca- ,2 pacity after destructive heating.

" ing to a heat treatment at temperatures from 150 to 275 C. for 2 to 90 hours duration.

The alloys must be manufactured with fine zinc with a purity grade of at least 99.9% Zn, wherein the remainder may consist of 0.080% lead, less than 0.005% tin and less than 0.020% cadmium. In the main, as the cadmium and tin contents are lower, the lead content can be higher (Pb max. 0.1 with Cd=0,'Sn=0). The alloys may further contain no magnesium content over 0.01%, preferably not over 0.005%, and no iron content above 0.1%.

-- not only dependent upon the heating temperature but also upon the copper content. The values. given in the following table for the heating temperature represent merely optimum values and the invention is not limited to them. The table principally illustrates the connection between the heating temperature, the copper content and the.

Patented May 2, 19.61

In particular, the alloys between heating time. As the example given above indicates, shorter heating times suffice to give usable results.

The clearly more satisfactory results with a copper content of the aluminium content correspond to. lower hardness of the alloy.

If the recommended heating is carried out more than once, a further important advantage for the bearing properties of the metal alloys is a successive lowering of the thermal coefficient of expansion with the number of'heatings. Whereas a non-tempered material in the region of from 20l00 C. has a linear thermal coefficient of expansion of 2325 10" the latter diminishes with further heating to 2022 10- After a second'heating, it diminishes to 1820 10 The effect of further heatings is always less and it depends upon the particular intended purpose of how far the diminution so obtained is in a definite relation to the greater consumption, e.g. for precision bearings. As to the hardness of the alloys, a copper content of /1. to /6 of the aluminium content is best.

In order to accelerate the decomposition process on heating, the temperature can fluctuate during the heating between 15 and 275 C. With this fluctuating heating, the temperature naturally must not go below 150 C. nor rise above 275 C., but the temperature can fluctuate over a range which lies between these two values.

A case hardening, i.e. heating above 275 C., by which the structure becomes homogenised, is to be avoided, since an alloy of the desired composition with a homoeneous structure is unsuitable as a bearing material.

Finally, it may be mentioned that it has not previously been possible to determine exactly whether the eutectoid shown in the diagram at c is obtained with 21% or 22% Al. The value of 21% is therefore to be considered only as'an approximation.

I claim:

l. A method of manufacturing a bearing material without homogenisation of the alloy structure thereof, which comprises subjecting a Zn/Al/Cu alloy, containing from 16 to 29% aluminum, at least 2.2% copper, the copper content being from to A1 of the aluminum content, and the remainder zinc, to pressing, and heat treating the resulting alloy at a temperature from 150 to 275 C. for a period' of from 2 to 90 hours, whereby case hardening is avoided.

2. A method of manufacturing a bearing material without homogenisation of the alloy structure thereof, which comprises forming a Zn/Al/Cu alloy containing from 16 to 29% aluminum, at least 2.2% copper, the copper content being from to A of the aluminum content, and the remainder zinc, and heat treating the formed resulting alloy at a temperature'from 150 to 275 C for a period of from 2 to 90 hours.

3. A hearing madeof a Zn/Al/Cu alloy having a nonhomogenised alloy structureland containing from 16 to 29% aluminum, at least 2.2% copper, the copper content being from to A of the aluminum content, and the remainder zinc, said alloy having been heat treated at a temperature of from 150 to 275 C. for a period of from 2 to 90 hours.

4. A hearing cast from a Zn/Cu/Al alloy having a nonhomogenised alloy structure and containing from 16 to 29% aluminum, at least 2.2% copper, the copper content being from A to,% of the aluminum content, and the remainder zinc, the cast alloy having been subjected to a temperature of from 150 to 275 C. for a period of from 2 to hours.

5. A method of manufacturing a bearing material without homogenisation of the alloy structure thereof, which comprises subjecting a Zn/Al/Cu alloy, containing from 16 to 29% aluminum, at least 2.2% copper, the copper content being from A to A of the aluminum content, and the remainder zinc, to casting, and heat treating the resulting-alloy at a temperature from to 275 C. for a period of from 2 to 90 hours, whereby case hardening is avoided. V p

6. A method according to claim 5 wherein the alloy contains from 18 to 26% aluminum.

7. A method according to claim 5 wherein the copper content of the alloy amounts to A to /6 of the aluminum content. s

8. A method of manufacturing a bearing material without homogenisation of the alloy structure thereof, which comprises subjecting a Zn/Al/Cu alloy, containing from 20 to 22% aluminum, at least 2.2% copper, the copper content being from to A of the aluminum content, and the remainder zinc, to casting, and heat treating the resulting alloy at a temperature from 200 to 270 C. for a period of from 3 to 24 hours.

9. A method according to claim 8 wherein the copper content of the alloy amounts to A to /6 of the aluminum content.

10. A'method of manufacturing a bearing material without homogenisation of the alloy structure thereof, which comprises subjecting aZn/Al/Cu alloy, containing from 16 to 29% aluminum, at least 2.2% copper, the copper content being from to A1 of the aluminum content, and the remainder zinc, to casting, and, heat treating the resulting alloy at least twice at a temperature from 150 to 275 C. for a period of from 2 to 90 hours each.v

11. A method of manufacturing a bearing material without homogenisation of the alloy structure thereof, which comprises subjecting a Zn/Al/ Cu alloy, containing from 16 to 29% aluminum, at least 2.2% copper, the copper content being from to A of the aluminum content, and the remainder zinc, to casting, and heat treating the resulting alloy at a temperature fluctuating within the range of from 150 to 275 C. for a period of from 2 to 90 hours.

12. A method of manufacturing a bearing material without homogenisation of the alloy structure thereof, which comprises subjecting a Zn/ Al/ Cu alloy, containing from 20 to 22% aluminum, a copper content from A1 to of the aluminum content and the, remainder zinc, to casting, and separately heat treating the resulting alloy at least twice at a temperature within the rangeof from 200 to 270 C. for a period of from 3 to 24 hours each.

13. A method of manufacturing a bearing material without homogenisation. of the alloy structure thereof, which comprises subjecting a Zn/Al/ Cu alloy, containing from 20 to 22% aluminum, a copper content from A to A; of the aluminum content and the remainder zinc, to casting, and heat treating the resulting alloy at a temperature fluctuating within the range of from 200 to 270 C. for a period of from 3 to 24 hours.

References Cited in the file of this patent FOREIGN PATENTS Great Britain May 16, 1956 Canada July 31, 1956 OTHER REFERENCES 

2. A METHOD OF MANUFACTURING A BEARING MATERIAL WITHOUT HOMOGENISATION OF THE ALLOY STRUCTURE THEREOF, WHICH COMPRISES FORMING A ZN/AL/CU ALLOY CONTAINING FROM 16 TO 29% ALUMINUM, AT LEAST 2.2% COPPER, THE COPPER CONTENT BEING FROM 1/10 TO 1/4 OF THE ALUMINUM CONTENT, AND THE REMAINDER ZINC, AND HEAT TREATING THE FORMED 